An engine may be operated with a lean air-fuel mixture or diluted (e.g., via exhaust gas recirculation (EGR)) to improve engine fuel economy and/or emissions. However, combustion stability may be reduced when an engine is operated with a lean or diluted mixture. One way to improve combustion stability for an engine that is operated lean may be to increase spark energy. Spark energy may be increased via increasing the inductance of a coil supplying spark to the engine via a spark plug. Nevertheless, increasing coil inductance can increase coil charging time, and higher inductance coils may reduce ignition system efficiency for conditions when increased amounts of spark energy may not be desired (e.g., during combustion of a stoichiometric mixture). These and other short comings of single coil ignition systems may be overcome by supplying spark to a spark plug via two ignition coils. The two ignition coils may be charged and/or discharged at different times to increase spark duration and energy, but operating two ignition coils for each spark plug at different times may significantly raise a number of controller outputs and wires. Consequently, a dual coil per spark plug system may improve combustion stability, but it may also increase system cost, complexity, and assembly time.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for providing spark to an engine, comprising: supplying two different ignition coil dwell times via a single conductor, the two different dwell times supplied to a first ignition coil and a second ignition coil; and discharging the first ignition coil and the second ignition coil to a single spark plug.
By encoding ignition coil commands, it may be possible to reduce a number of conductors in an engine ignition system. In one example, ignition coil commands for one ignition coil are based on pulse widths that are greater than a first predetermined time. Ignition coil commands for a second ignition coil are based on pulse widths that are less than a second predetermined time. The two different pulse widths may be transmitted over a single conductor to operate two ignition coils supplying energy to a single spark plug.
In another example, commands for a first ignition coil may be transmitted over a first conductor while commands for a second ignition coil may be transmitted over a second conductor. The second conductor may also carry commands for a plurality of other ignition coils supplying energy to spark plugs in other engine cylinders. Thus, fewer conductors carrying ignition coil signals than ignition coils may be incorporated into an ignition system. As a result, ignition system wiring complexity may be reduced.
The present description may provide several advantages. In particular, the approach reduces ignition system wiring complexity. Further, the approach may reduce ignition system assembly time. Further still, the approach may reduce ignition system cost.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.